1. Field of the Invention
The present invention relates to an evaporated fuel treatment device for a vehicle, and more particularly to an evaporated fuel treatment device for a vehicle which introduces an evaporated fuel generated in the inside of a fuel tank to the outside of the fuel tank by making use of a fuel supply cap.
2. Background of the Invention
JP-A-5-246367 discloses a fuel supply cap of a fuel tank for a motorcycle provided with an evaporated fuel treatment device. The fuel supply cap includes a positive pressure adjusting valve which opens when a tank inner pressure becomes a predetermined pressure or more, and a liquid leakage preventing valve which prevents the flowout of fuel (see JP-A-5-246367 in FIG. 4). The positive pressure adjusting valve in the fuel supply cap is communicated with a canister in the fuel supply cap, and an inner pressure of the fuel tank can be transmitted to a canister side by opening the positive pressure adjusting valve.
In the fuel supply cap of JP-A-5-246367, the positive pressure adjusting valve and the liquid leakage preventing valve are separately provided and are arranged parallel to each other in the lateral direction of the fuel supply cap. Therefore, the size of the fuel supply cap becomes too large. Further, in such a fuel supply cap, a spherical valve is used as a valve for preventing liquid leakage. However, when such a spherical valve is used, it is necessary to take into account the structure which prevents sticking of a spherical body to a valve seat. Also in the constitution where the positive pressure adjusting valve and the liquid leakage preventing valve are arranged parallel to each other in the lateral direction, an attempt to further improve the sticking prevention structure gives rise to a drawback that the fuel supply cap becomes more even larger and complicated. In addition, although the liquid leakage preventing valve is provided to the fuel supply cap, when a fuel tank is inclined, a liquid pressure of fuel is applied to the positive pressure adjusting valve so that fuel intrudes into a canister from a positive pressure adjusting valve side. This weakens the absorption ability of the canister.
On the other hand, although only the positive pressure adjusting valve is provided to the fuel supply cap according to JP-A-5-246367, to reduce the diffusion of evaporated fuel in the tank to the outside, it is desirable to also provide a negative pressure adjusting valve which opens when a tank inner pressure becomes a predetermined pressure or less. However, when the negative pressure adjusting valve is provided to the above-mentioned fuel supply cap in addition to the positive pressure adjusting valve, the fuel supply cap becomes further larger, thereby making the application of the evaporated fuel treatment device to a miniaturized vehicle difficult and/or impossible.
In addition, in the fuel supply cap of JP-A-5-246367, the liquid leakage preventing valve is always communicated with atmospheric air (canister).